A pacemaker lead extends from the subcutaneous tissue pocket where a pacemaker is positioned through a vein and into a chamber of the heart. Similarly, defibrillator leads are affixed to the heart both internally and externally. Over time, the lead becomes encapsulated by fibrotic tissue against the wall of the vein or surrounding tissue. The tough, fibrotic tissue makes it difficult to remove a lead from the vein. Furthermore, removing a lead from this fibrotic tissue presents the risk of complications such as injury to the vein and bleeding. To avoid complications, some useless pacemaker leads are left in patients when a pacemaker is removed and replaced. On the other hand, life-threatening complications can require the removal of a pacemaker lead from the vein of a patient. For example, if a pacemaker lead becomes infected, septicemia and endocarditis can result; if there are too many leads positioned in a vein, the vein can be obliterated; if multiple incompatible leads are positioned in the same vein, they can interfere with the pacing function; and if a lead migrates, mechanically induced ventricular arrhythmias can occur. Furthermore, it is beneficial to remove a lead from a patient when removing and replacing a pacemaker due to the risk of undetected lead thrombosis which can result in stroke, heart attack, or pulmonary embolism.
Pacemaker leads are typically removed from the vein of a patient using a dilator sheath. Commonly, two coaxial dilator sheaths are positioned over the lead and advanced therealong for loosening the lead from the fibrotic tissue on the vein wall. Some dilator sheaths are formed from plastic tubes, which are flexible for bending around the natural anatomical curvatures of the vascular system. A problem with the plastic dilator sheaths is that the leading edge of the dilator sheath is weak and can lose its edge and buckle onto the lead during use. As a result, the plastic dilator sheath is damaged and unusable before the lead is loosened from the fibrotic tissue. Furthermore, flexible plastic sheaths commonly kink when subjected to tough fibrotic tissue. This problem is further heightened when the sheath is bent around a vessel curve. Other dilator sheaths are formed from metal tubes, which include a sharp leading edge for encountering fibrotic tissue. A problem with the metallic dilator sheaths is that they are relatively inflexible and resist bending around natural anatomical curvatures. As a result, the metallic dilator sheaths can be difficult or impossible to advance toward the distal end of the pacemaker lead without injuring or obliterating the vein. Plastic sheaths with metal tips are also known; however, kinking problems still exist for the flexible plastic portion as well as there being a concern for the metal tip detaching from the main plastic body.